Contemporary analytical instrumentation is frequently capable of producing multi-channel data which can be related to the concentration of analyte in a sample (referred to herein as quantitative analysis) or the identity of one or more materials present in a sample (referred to herein as qualitative analysis). Examples of instruments capable of producing such data include Infrared and Raman spectrometers, Mass spectrometers, X-ray Fluorescence (XRF) spectrometers, and Nuclear Magnetic Resonance (NMR) Spectrometers. Within the scope of qualitative analysis, there are several types of assessments that can be performed.
One type of qualitative analysis assessment is authentication which examines whether the measured instrument response is consistent with one or more reference library signatures for a specific material of interest. Said differently, this type of analysis aims to determine if the test material spectrum is consistent with a genuine substance. Examples of applications where authentication is performed include evaluation of raw materials received from a supplier to determine whether the correct ones were provided, examination of a tablet to determine whether it is genuine or counterfeit, and analysis of a material to determine whether it has been adulterated, spoiled, etc.
Another type of qualitative analysis assessment is screening which evaluates whether at least a subset of features in the measured instrument response correspond to one or more specific substances of interest. This type of assessment evaluates whether the test material appears to contain a particular substance. Screening can be used by those with a very small set of analytes of particular interest, such as narcotics, explosives, or materials of environmental concern. In a screening assessment it is not necessary to determine the identity of materials that are not in a watch list. For example, it may be important to know whether a children's toy contains lead but it is not necessary understand what type of plastic, wood, or metal are present.
Yet another type of qualitative analysis assessment is identification which is performed by scouring a library of known materials and looking for similarities between the unknown instrument response and the stored responses for known materials (or combinations of stored responses for known materials). Such an assessment assumes the user does not know what they are testing for, and thus wants to know “what is this material?”. Computer-aided identification is frequently referred to as “automated spectral searching”, and is frequently used in scenarios such as hazardous material (hazmat) calls and laboratory investigations.
From the above descriptions, it can be noted that the authentication problem is designed for users with a very specific need (those who know exactly what they are testing for). On the other hand, the screening and identification problems are much less bounded. Given the extremely broad applicability that identification apparatus provides, it may be noted that they can be used to identify any analyte that a screening apparatus might be configured to detect, plus many more. There are two principal advantages of screening that compel users to forgo the broad applicability provided by identification: screening algorithms can typically be configured to have higher detection rates and lower limits of detection than identification algorithms, and a screening apparatus can be configured to provide a user with visual and/or audio cues that a specific material of interest has been detected. When an identification application detects a material, it does not call specific materials out as more important or concerning than other materials.